I'd definitely make a training program of just groundwork - as if she's a young horse - teach her to lead, stand, back, move left, move right... Move on to tacking up calmly (head down, standing still), lunging, etc. etc. She may have very little training in basic manners, on top of being abused and untrusting. Even if she does a skill already, re-teach her to do it properly as though she doesn't know. It'll give her a regular work routine to help calm her, and teach her to pay attention to everything you ask. If you spend a couple months on that, I would imagine her calmness and trust will improve overall, and the cross-tie problem will diminish and could be re-taught with less panic.